In modern surgery, one of the most important instruments available to medical personnel is the powered surgical drill. Typically, this drill comprises a housing in which a motor is secured. The motor has a shaft that is connected to some type of chuck or other coupling assembly attached to the housing. The coupling assembly holds a cutting accessory that is applied to the patient in order to perform a specific medical procedure. Some common cutting accessories are drill bits, burs and reamers. These accessories are used to drill into and/or separate sections of soft tissue and hard tissue, commonly referred to as bone. The ability to use surgical drills to actuate these and other cutting accessories has lessened the physical strain of physicians and other medical personnel that perform these medical procedures. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.
Surgical drills are often used in certain orthopedic surgical procedures in order to facilitate the repair of fractured and broken bones. These fractures and breaks typically occur as a result of trauma to the bone. In this type of procedure it is practice to fit a pin or screw to the adjacent sections of the bone so as to hold these sections together. In this type of procedure, the drill is used to form a bore hole/holes in the section/sections of the bone in which the pin or screw is to be fitted.
In this type of procedure, the drill bit, while it should extend through the bone, should not be pressed beyond the bone. This is because if the tip of the drill bit, presses through the bone, the tip could damage the soft tissue adjacent the bone. This damage is more likely to occur if the tip, when pressed against the soft tissue, is rotating. This soft tissue, it should be appreciated, includes both neurological tissue and blood vessels. While it is always in the best interest of the patient to avoid damaging any tissue, it is even more important to avoid damaging nerves and blood vessels.
Accordingly, when a surgeon is forming a bore in bone in order to set a pin or a screw, the surgeon must typically use extreme care to ensure that, as soon as possible after the drill bit tip penetrates through the bone, the drill is deactivated.
One means suggested to reduce the extent to which a rotating drill bit is allowed to press into soft tissue adjacent a bone is to provide trauma surgeons with drills similar to the cranial perforators used by neurosurgeons. A cranial perforator is the type used by a neurosurgeon in order to form the initial entrance opening into the skull. A cranial perforator includes a head and inner and outer drills. The inner drill is in the form of a solid cylinder that is fluted at the distal end. The outer drill is in the form of a sleeve that extends circumferentially around the inner drill. Both drill bits extend from the head. The head is attached to handpiece having a motor. Internal to the head both the head and the drill bits have features that, when engaged, causes the drill bits to rotate with the rotation of the head. Also internal to the head is a spring. The spring normally holds at least one of the drills away from the complementary features integral with the head. When the drill bits are pressed against bone, the resistance of the bone pushes the drill bit and head features into engagement. When the perforator is in this state, the rotation of the head results in a like rotation of the drills. The rotational moment and forward force of the drills causes the drills to form the desired bore. When the inner drill, penetrates through the skull, the skull no longer offers resistance to the release action of the spring. The spring pushes the inner drill away from the head. Owing to the engagement of the outer drill with the inner drill, the outer drill also stops rotating. Thus, when the perforator is in this state, the rotation of the head does not cause a like rotation of the drill bits. Since the drills are not rotating when the perforator is in the this state the pressing of the drills against the tissue, the thin soft tissue below the skull does not result in appreciable damage to this tissue. In many versions of the invention the head and drill bits are formed with complementary ramp features. These ramp features facilitate the disengagement of the drills from the head. A more detailed understanding regarding how a cranial perforator operates can be found in the Applicant's Assignee's US Pat. Pub. No. US 2009/0024129 published 22 Jan. 2009, the contents of which are explicitly incorporated herein by reference.
One reason cranial perforators work well for forming bores in the skull is that the skull is relatively thin. Typically the skull has a thickness of 1.5 cm or less. Thus, once the bore is formed, the surgeon, with using only a minimal amount of force, can pull the perforator out of the newly formed bore.
In trauma surgeries and other orthopedic surgeries the surgeon may want to form a bore hole in bone that is relatively thick, having a thickness of 3.0 cm or more. Owing to the tight fit of the drill bit in the bore, it is rather difficult to simply pull the bit out of the bone. If a practitioner uses a large amount of manual force, there is the possibility that the use of this back force, especially if coupled with a back and forth prying action, can damage the bone. This force if strong enough can also damage the drill bit.
To avoid the possibility of this post bore formation bone damage, an orthopedic surgeon typically drives the drill bit in reverse in order to facilitate the backing out of the bit from the bore. However, as mentioned above, once the drills of a cranial perforator penetrate the bone, they are disengaged from the complementary head. Driving the head in reverse does not foster a like rotational movement of the drills. This is why cranial perforators, while useful for preventing damage to the tissue underlying the bone against which they are pressed have not proven particularly suitable for forming the relatively deep bores required by orthopedic surgeons.
Another problem with the use of cranial perforators is that during the formation of a bore, the drill bit may disengage from the motor before the bore is completely formed. The orthopedic surgeon may need to remove the drill and then re-drill the bore again to complete the formation of the bore.
Moreover, once the bore is formed, it is desirable to determine its depth. This aids the surgeon in determining the length of the pin or screw that needs to be fitted in bore. Current depth gauges take the forms of a rod with a distal end step. The rod is placed through the bone bore and moved until the step catches on the bone adjacent the bottom of the bore. The surgeon then reads the depth from a shell to which the rod is slidably mounted. Often these depth gauges are designed so that the step is very small in width, 2 mm or less. This makes positioning the rod so that step catches a time consuming task.
Thus, to perform this measurement, the surgeon must first delicately position the wire to ensure that the hook does not damage tissue underlying the bone. Then, to accurately make the measurement, the surgeon must both carefully position the wire and his/her finger against the wire. Having to carefully perform these steps can add to the overall it takes to perform the procedure.